ORA-01115 IO error reading block from file string

We have started experiencing this error in the last few weeks and are
trying to identify the cause. We opened a ticket with Oracle and one
with HP (SAN).I just checked the logs from the web servers and found
this ORA-01115 error was logged by the web application 6 times yesterday
between 2:49 and 3:10 PM. We're not sure if it's both nodes or just
one. The last time it had been logged previously was 12/22/05. Four of
those times, it was the same file that our batch process had a problem
with -- PARTIES_DATA01.dbf. On the other 2 occasions, it was
PARTIES_DATA02.dbf and LOCATION_DATA01.dbf.

HP says the SAN is healthy, Windows hasn't logged any issues, and Oracle
says it isn't their problem. If anyone has a suggestion for diagnosing
this, I'm all ears.

ORA-01115 IO error reading block from file string (block # string)
Cause: The device on which the file resides is probably off line.
Action: Restore access to the device, then retry the operation.